The Best Subsea Cable Across The English Channel: Scylla

The English Channel has been a sore spot for the wholesale telecommunications industry. The key problem is the abundance of freight and fishing vessels. Ships are the number one global cause of subsea cable outages. They drop their anchors to come to a halt and also drag them to maintain stability in rough seas. For example, last autumn a Chinese freight ship called the New New Polar Bear dragged its anchor through the Baltic Sea knocking out a gas pipeline as well as the fibre optic cable attached to it. This Spring a Houthi missile hit the Rubymar cargo ship in the Red Sea; consequently, the crew abandoned ship. To do so, they dropped the anchor to halt the vessel so the crew could safely depart in the life boats. Afterwards, the Rubymar drifted 31 kilometers and its anchor severed 3 major subsea arteries of European/Asian traffic, namely the AAE1, EIG, and jointly owned Seacom/Tata cables. It took five months to get those three cables fixed due to the ongoing Houthi rebel conflict. Fishing is another notorious submarine cable predator. Most continental shelf fishing involves scraping the sea floor and trawlers have damaged many subsea cables as a result despite strenuous efforts to educate the fishing industry about where the cables are located so they can be avoided.

The English Channel cables have had not surprisingly a lot of outages and repairs. Furthermore, most of them are quite old as they were built during the 1998-2001 dotcom era. Lots of repairs means lots of  splicing which inevitably increases end-to-end signal loss and shortens the cable's life span. Probably the best protected and most reliable path across the English Channel is the Chunnel. This underground railway tunnel was carved out of solid rock 75 meters below the sea floor iith a layer of clay above it that protects it from sea water seepage. However, best network design practice dictates having two fully diverse paths to connect London to Continental Europe, typically the Paris/London and London/Amsterdam routes. The Chunnel's obvious complement in a diverse design is EUNetwork's Scylla cable. Another candidate is Zayo's Zeus, which I will talk about it in a separate post. Scylla is a three year old unrepeatered double armored 96 pair system that connects the Netherlands to the UK, but has yet to experience its first outage since going live September 9, 2021. The cable's exceptional performance reflects an excellent sea floor survey and remarkably deep 3 meter burial. Careful and detailed sea floor surveys are essential to avoid areas that have exposed hard rock that can destroy a subsea plough or drill bit, subsea canyons which are notoriously prone to debris slides, fishing grounds where trawlers operate or archeological sites like ship wrecks, etc.  The 3 meter burial depth may seem excessive, but anchors generally sink deep into the silt at the bottom of the sea given their 5 to 10 ton weight and so very deep burial is your best shot at avoiding damage and outages. Sea floors are generally muck, not rock, as organic matter is constantly being deposited due to the earth's well-known carbon cycle. 😀 Undoubtedly, Scylla was an expensive build due to the deep burial. In fact, it may have required a special sea plough. The Scylla cable should be a building block of your network if it connects the UK to Continental Europe. It is the most reliable subsea network across the English Channel and also is very high capacity which equates to bandwidth scalability and good pricing. It also the lowest latency path London/Amsterdam. 

It is worth noting that 96 fibre pairs is a lot of potential bandwidth. Scylla's length is 211 kilometers. Unrepeated systems over that distance can generally do at least 20 terabits per pair. So a conservative estimate is two petabits of transmission capacity. That is a lot of bits. 😊 However, to be fair, I think per fibre pair throughput is more likely to be around 25 Tbps. So the cable probably can do up to  2.4 petabits per second. This is consistent with another unrepeatered English Channel cable, the Crosslake CrossChannel project, which has the same number of pairs and is reported to be capable of 2.4 petabits per second.☺